1. Field of the Invention
The present invention relates to a system and method for controlling a variable displacement engine to manage temperature of a catalyst system.
2. Background Art
Fuel economy for a multi-cylinder internal combustion engine can be improved by deactivating some of the engine cylinders under certain operating conditions. Reducing the number of operating cylinders reduces the effective displacement of the engine such that it is sometimes referred to as a variable displacement engine. Depending upon the particular configuration of the variable displacement engine, one or more cylinders may be selectively deactivated to improve fuel economy under light load conditions. In some configurations, a group of cylinders, which may be an entire bank of cylinders, is selectively deactivated.
Reducing the number of operating cylinders may also reduce the operating temperature of various engine and/or vehicle components, which may adversely affect desired engine operation. For example, certain emission control devices, such as catalytic converters, require a minimum operating temperature for efficient operation. One approach to raise catalyst temperature involves enriching the fuel supply to the operating cylinders when catalyst temperature drops below a specified level as disclosed in U.S. Pat. No. 4,467,602. This method assumes that excess air is available in the catalytic converter to be effective. The inventors herein have recognized that this assumption may not always be valid and may result in reduced catalyst and/or engine efficiency during certain operating conditions.